1. Field of the Invention
The present invention relates to an indium antimonide (InSb) photodetector device and photosensitive structure having a passivated light receiving surface which eliminates degradation of photoresponse in the infrared region due to flashing and enables the device to detect radiation in a continuous spectral range including the infrared, visible and ultraviolet regions.
2. Description of the Related Art
Back-side illuminated InSb photodetector devices such as photodiode arrays have been conventionally used for detecting infrared light radiation in a wavelength range of approximately 1-5.5 micrometers. However, they have been unusable for detecting light in both the infrared and visible regions due to a "flashing" effect which is inherent in conventional back-side passivated/anti-reflection coated InSb devices.
A conventional passivation/anti-reflection coating is formed by anodization of the back-side, or light receiving surface of the photodetector device substrate as described in an article entitled "Formation and Properties of Anodic Oxide Films on Indium Antimonide", by T. Sakurai et al, Japanese Journal of Applied physics, vol. 7, no. 12, December 1968, pp. 1491-1496.
The anodized oxide layer is predominantly microcrystalline In.sub.2 O.sub.3 and Sb.sub.2 O.sub.3 with a high concentration of antimony located interstitially within the oxide film. The antimony ions which are located close to the oxide/InSb interface form carrier traps. The flashing is caused by hot electrons generated by photons of visible or ultraviolet light which are captured by these electron traps in the passivation layer. The trapped electrons suppress the infrared response by recombining with photogenerated minority carriers (holes) before they are collected in the semiconductor P-N junctions of the device.
The prior art approach to utilization of InSb photodetectors for detecting infrared radiation is to provide a filter which selectively prevents light of visible and ultraviolet wavelengths from reaching the device. This, of course, renders the device inoperative for detecting visible and ultraviolet light.
The In.sub.2 O.sub.3 and Sb.sub.2 O.sub.3 oxides, in addition to any other oxides which may be formed through reaction of indium and/or antimony with oxygen, are referred to as "native oxides". The invention disclosed in the related application overcomes the flashing problem by eliminating these native oxides and associated carrier traps from the light receiving surface of an InSb photodetector, thereby producing a photodetector device which is capable of detecting visible and infrared light in a wavelength range of approximately 0.6-5.5 micrometers.
An antireflection coating is formed over the passivation layer. Although these layers are successful in performing their intended functions, they prevent the device from detecting radiation of wavelengths shorter than approximately 0.6 micrometers.